Fusible link



Oct. 30, 1962 w, HQDGMAN, JR 3,061,016

FUSIBLE LINK Filed Dec. 14. 1959 IIIIIIJIIIIII I \\\\W||Ill la is .lllll7/1. W

FIG. 2

' INVENTOR.

YWILLIS K.HODGMAN JR.

611-14. 5W v M ATTORNEYS United States Patent 3,961,016 FUSIBLE LINKWillis K. Hodgman, Jr., Taunton, Mass, assignor to Hodgman ManufacturingCo., Inc., Taunton, Mass., a corporation of Massachusetts Filed Dec. 14,1959, Ser. No. 859,413 1 Claim. (Cl. 169-42) This invention relates toimprovements in fusible links used in automatic sprinklers forextinguishing fires, or in other devices wherein it is desirable to holdcertain parts of the mechanism to which they are applied in assembledcondition until a predetermined degree of temperature exists in thevicinity of the apparatus and melts the solder uniting the parts of thelinks.

The objects of the invention are to provide a fusible link of superiorefliciency as to both its holding and releasing functions.

I attain these objects, in a fusible link of the three piece typeembodying the principle of the invention, by employing two opposedplates having relatively shoal transverse channels, substantiallyrectangular in cross section, which provide a chamber between the plateswhich is occupied by a fulcrum-block located half and half in each ofthe plates. The sides of the channels are made with the edges bevelledor rounded and may have rounded fillets where they join the bottoms ofthe channels. These radii are sufliciently small so that a straightportion is left on both sides of the channels, these straight portionsbeing substantially perpendicular to the common plane of the opposedplates. The fulcrum-block is substantially rectangular in cross-sectionand also has bevelled or rounded edges, the radii of which do not have acommon meeting point.

In order that the principle of the invention may be readily understood,I have disclosed a single type or embodiment thereof in the accompanyingdrawing, in which:

FIG. 1 is a side elevation of my link;

FIG. 2, a vertical section on line 22 of FIG. 1; and

FIG. 3 is a magnified view of the central portion of FIG. 2.

Similar numerals refer to similar parts throughout the several views.

My fusible link, as shown in the drawing, is of the three piece type andconsists of duplicate plates 4 and 5, a fulcrum-block 6 and a fusiblesolder which melts at a predetermined degree of heat. The solder isapplied between the opposed surfaces of the parts of the link in theusual manner but is not shown in the drawing.

Each of the plates is provided, near its outer end, with an aperture 7to receive one of the parts to be held in assembled condition, shown inthe drawing as the end of one of the levers 8 or 9 (shown in FIG. 2,only) of a usual type of automatic sprinkler (not shown).

The inside face of each plate about midway of its length is providedwith a transverse channel 10, of an approximately rectangular crosssection with the flat parts of its sides perpendicular or nearlyperpendicular to the face of the plate. The edges of these channels arebevelled or rounded as shown at 4a and a and may have rounded filletswhere the sides join the bottom of the channel. In the drawings, theselatter corners are shown, however, as perpendicular.

The fulcrum-block 6 is of slightly less width over all than the width ofeach channel 10 thus being free to tilt and pry the plates 4 and 5 apartwhen the solder melts, and has rounded corner edges as shown at 6a. Thethickness of the fulcrum-block is twice the depth of each channel so itis normally located half and half in the channels. The rounded orbevelled edges 6a of the fulcrumblock are relatively short and leaveopposed flat surfaces, indicated at 11 in FIG. 3, bearing against eachother at definitely predetermined distances from the plane of the flatabuting inner surfaces of the link plates. The object of thisconstruction is to provide a definite turning moment or tilting to thefulcrum-block since the bearing surfaces of the fulcrum-block edges makecontact with the adjacent sides of the channels in the link plates onopposite sides of the plane of the inside surfaces of the link plates.

The resulting tendency of the link plates to be thrown apart when thesolder melts is in the ratio of between the limit-s 5 to l and 10 to 1.That is, if a pressure equal to 1 unit is imposed on the assembledunsoldered link to hold the plates together, it takes a longitudinalpull applied at the apertures 7 of from 5 to 10 units to rock thefulcrum-block thereby throwing the link plates apart.

When the link is assembled the channels in the plates overlap and thefulcrum-block is mounted in that portion of the chamber formed by theoverlapped portions of the channels. The fulcrum-block 6, it will benoted, is symmetrical with respect to a plane extending midway thethickness of the block. Hence the fulcrum-block may be placed inposition with either edge up or down and with either longer face againstthe bottom of either channel. The fulcrum-block is thus reversible bothedgewise and endwise. This is of material advantage in assuring thecorrect assembly of the link because it is impossible by reason of thissymmetrical form of the fulcrum-block to place it in the wrong position.

In addition, it will be noted that the radii of the corner edges 4a and5a of the channels 10 are easily controlled to close tolerances and thattheir contour permits long wear for stamping dies employed infabricating them. Thus, since it is the distance from the plane ofabutment between the plates 4 and 5 to the point of contact with thefulcrum-block 6 which determines the wedging apart leverage of the link,and since this distance is determined by these radii, this exact controlfeature adds to the desirability of using this construction set forthherein. The edges 4a and 5a need not be round but can be bevelled orfaired and I shall use the term truncated in the claim to define anysuch equivalents generically.

It will also be noted that rounding the corner edges 6a of thefulcrum-block 6, permits a free tilting of the block 6 which wouldotherwise be hindered by friction, surface tension and/ or a suctioneffect of the liquid solder if the corner edges 6a were sharp.

With the link assembled and the parts soldered together, thelongitudinal pull applied at apertures 7 is taken mostly by thefulcrum-block thereby producing a link of great holding power until thesolder is melted or fused by heat. When this takes place, thefulcrum-block tilts and insures the immediate separation of the platesso that the link falls apart at once.

Having thus described one illustrative embodiment of my invention, Idesire it to be understood that although specific terms are employed,they are used in a generic and descriptive sense and not for purposes oflimitation, the scope of the invention being set forth in the followingclaim.

I claim:

In a fusible link having identical link plates disposed in assembledcondition in face to face relationship and sealed together by a fusiblematerial; a substantially rectangular transverse channel formed in eachsaid plate, said channels being opposed to each other when said platesare in assembled condition; each said channel having a top wall and abottom wall, each said wall being normal to the face of said plate, anda side wall parallel to said face of said plate joining said top walland said bottom wall; said substantially rectangular transverse channelsbeing provided with rounded edges formed at the juncture of said topwall and said bottom wall with the said face of said plate, said roundededges extending only a slight distance along the adjacent surfaces; andfurther including a fulcrum block normally residing Within said opposedchannels, said fulcrum block being substantially rectangular incross-section and having a substantially fiat top face, a substantiallyflat bottom face, a first side face, and a second side face, said topand said bottom faces being parallel to each other and said first andsaid second side faces being parallel to each other; said fulcrum blockfurther having rounded edges and being of substantially the same widthas the combined width of said channels to abut said sides of saidchannels at said first and said second side faces of said fulcrum blockand further having a vertical dimension such that said top wall of oneof said channels abuts said substantially fiat top of said fulcrum blockand said bottom Wall of said other of said channels abuts saidsubstantially fiat bottom of said fulcrum block, said points of abutmentbeing in each instance inwardly in said chanme] from said rounded edgethereof and inwardly on said fulcrum block from said rounded edgethereof, whereby when said fusible link is in assembled condition and aforce is exerted on said link plates along the center line of the planeof said abutting faces thereof to draw said plates apart, said forcewill be exerted upon said fulcrum block through said link plates atportions of said top and of said bottom of said fulcrum block spaced offcenter on opposite sides of the center line of said fulcrum block toimpart a turning moment to said fulcrum block to cause instantseparation of said link plates upon melting of said fusible material.

References Cited in the file of this patent UNITED STATES PATENTS725,495 Shaw et a1 Apr. 14, 1903 1,155,339 Cook Oct. 5, 1915 1,308,075Hopkins July 1, 1919 1,356,919 Hopkins Oct. 26, 1920 1,452,522 Nacy Apr.24, 1923 1,520,750 Hodgman Dec. 30, 1924 1,539,311 Hodgman May 26, 1925

